Tuning circuit for high-frequency receivers



July 12, 1949.

J. A. WORCESTER, JR

TUNING CIRCUIT FOR HIGH-FREQUENCY RECEIVERS Fil ed Sept. 28', 1946 Inventor": Joseph A. Worcester; Jrr,

His Attorney.

Patented July 12, 1949 UNITED STATES i ATENT OFFICE TUNING CIRCUIT FOR HIGH-FREQUENCY RECEIVERS Joseph A. Worcester, J r., Fairfield, Conn., assignor to General Electric Company, a corporation of New York Claims.

1 My invention relates to apparatus for receiving high frequency waves and, in particular, for receiving a plurality of bands of short waves, some of which are modulated in amplitude and others of which are modulated in frequency. The primary object of my invention is to provide new and improved circuits for tuning radio receivers over a plurality of bands.

It is another object of my invention to provide a new and improved tuning circuit for radio receivers in which a variable element employed for tuning over one of a pair of bands of high frequencies is utilized as a device for spreadtuning over the other band of high frequency Waves.

It is still another object of my invention to provide a new and improved multi-band receiver in which a single variable tuning element is utilized for tuning the circuits of the receiver over allof the high frequency bands of the receiver.

One of the features of my invention consists in connecting a variable inductance, which is employed to tune a radio receiver over a first band of high frequencies, in series with a fixed inductance, the range of the tuning inductance being restrictedby a sufficient amount to allow the circuit to be tuned over the rangeof another band of high frequencies.

Still another feature consists in employing similar tuning arrangements in both the oscillator and radio frequency circuits of a receiver adapted to receive both amplitude modulated high frequency waves of short wave length and frequency modulated waves, the circuits being adjusted for the reception of a particular band by merely controlling the connection of a fixed inductance in series with a variable inductance.

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims. My invention itself, both as to its organization and method of operation, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawing in which Fig. 1 is a circuit diagram of a portion of the high frequency circuits of a multi-band radio receiver embodying my invention, and Fig. 2 illustrates a vane tuner suitable for use in the circuit of Fig. 1.

Referring to Fig 1, I have shown the high frequency portion of a multi-band radio receiver as comprising an antenna tuning circuit l which is utilized for translating signals to a radio frequency tuned circuit 2. The output-o1? the radio 2 frequency circuit 2 is supplied to a frequency converting tube 3 Where the high frequency signals are mixed with oscillations generated locally in a resonant circuit 4. The antenna tuning circuit l is connected through a coupling capacitor 5 to an input terminal 6 to which are supplied received high frequency signals from the usual antenna. The antenna circuit 1 comprises an inductance 1 having its lower terminal connected to ground and its upper terminal connected to a multi-position band switch 8 having a plurality of fixed contacts 9H and a movable contact or arm [2. The upper terminal of inductance l is likewise connected to the fixed contacts [0, ll of a second multi-position band switch l3. In the switches 8, 13, as well as other switches employed in my circuit, the fixed contacts at corresponding positions are designated by like reference numerals. The inductance 1 is utilized as the variable reactance element of the tuned antenna circuit I and is varied in value by means of a tuning element [4 which may be,

for example, a ferromagnetic core adapted to be varied in position within the turns of the inductance fl. Preferably the inductance I is of the type disclosed in the copending application of E. 0. Peterson and E. W. Forstrom, Serial No. 698,350, filed September 20, 1946, and assigned to the assignee of the present invention. An inductance of this type comprises a pair of juxtaposed peripherally incomplete serially connected metallic conductors. The tuning element IQ for an inductance of this type comprises a metallic vane adapted to be varied in position ,between the conductors to control their self and mutual inductance.

When the switch 8 is in the position shown in the drawing, the variable inductance 1 is shunted by a trimmer capacitor I5 which is connected between the contact 9 of a multiposition band switch It and ground. The movable contact 12 of switch [6 is directly connected to the movable contact H of switch 8 and through capacitor 5 to the input terminal 6. When the switches 8, I 3, which are ganged together for unicontrol operation, are moved to positions I0, II, a fixed inductance I1 is connected between contact-s Ill, ll of the respective switches and in series with variable inductance I. The inductance 1 preferably is of such a value that it is resonated by the trimmer capacitor l5 over a band of frequencies employed for frequency modulated signals, This inductance is so increased by the insertion in the circuit therewith of the fixed inductance I! that the resultant inductance lengths is effected by movement of the tuning,

element l4 relative to the winding 1, the induct ance I! being of a value that it resonates with the trimmer capacitors in the-desired" short. wave band. The movement of theelement l4 relative to the winding I is effective to spread the tuning of the antenna circuit l over these respective band-s.

The antenna circuit l is connected to the control electrode of an electron discharge device 21; having a cathode 2 2'. connected. to ground through. abias, resistor. 23.shunted by a capacitanoel24. The anode-25 of'device 2| is supplied.

with operatingpotential fromiany. suitable source indicatedby the legendB+ through a choke 26 connected to the source. B.+ through a multi-po- 'si tion switch 21 When the switch 21 isconnected to-contact 9' thereof, the. inductance 26., which is of vrelatively low value, is; directly connected. to the.;sour,ce. B+. However, when the switch 21 is connected to the contacts, l.0=.a nd ll, inductance- 26; is. connectedto the source through a series choke 28: having a larger value of inductance. Anode 25 is connectedsthrough a, coupling capaci term to the upperiterminal of inductance 30' in the, tuned radio frequency circuit Z. The selfinductance of the inductance 30, which is similay; in construction to-inductancel; is adapted. to be variedin value by means'of a tuning element 3!. and the, lowenterminal of inductance. 30 is A can ectedtogroundt The tuned radio frequency. circuit-i is identicalwith the tuned antenna circui t Il -and includes an inductance 32 whoseconnections correspond .tothose of inductance lilr in the antenna circuit, a plurality of multiposition switches 33,. 34, 3.5,: corresponding.respectively to.

switchesfl. l.3 .-and I6 and a plurality of trimmer capacitors i -38;having;-valuesv and functions corresponding to thos e of capacitors. I 5, l8, and I 9.- Th ,converter tube-3.;is illustrated as ofa the pentagrid type having a control electrode 39 .-to

which the tuned .R; F. circuit 2 is. directly connected The local oscillator circuit'll-isconnected between .acontrol grid 40 and cathode42, while.

anode-4i of. converter 3 is connectedtoan output or intermediate frequency circuitfiae he screen.

cuitgd comprises an inductance,-4.whichis adapta ed}: to. be. varied in-value. by means of. a movable tuning .elementA]. Qneiterminal of theinducte ane'e AQ is conneotedtoground, and. the other tenminal connected to, contact 9 of the mu1ti posi tion switch lfi. Thfipther terminalpf, inductance 46 isnlikewise connectedto contacts .I ll, and 1 l of.

alswiteh 4a. rhem yabie Conta t .of switch ism is .r e e i J 0-, A f mi a? -me emee 4 of the switches 48, 49, therefore, the inductance 5| is either removed from the receiver circuit or is connected therein, with its upper portion connected in series with variable inductance 4B and its portion between tap 50 and ground connected in shunt with inductance 46. I provide a plurality of capacitances 52-54: for resonatin the oscillatorcircuit to a desired frequency band depending upon the band of waves desired to be received by the receiving apparatus. The capacitances. 51-54- are/connected, respectively, to the contacts 9-H of a three-position switch 55 in order that they may easily be shunted across the inductance selected'by switches 48, 49. Capacitan-cesE-i and 54 have their lower terminals connected to ground, while capacitance 52 is connected to groundthrough a choke 56 shunted by a capacitor 51. The common terminals of inductance 56 and capacitors 52, 51 are connected to the contact 9 of a multi-position switch 58. The? contacts I0 H; of switch 58 are connected tocthei intermediate tap 50.011 inductance. 5:1; while: the movableycontact of switch. 58=- is connected directly to-the cathode-42.; Cathode-42 is likewise 1 connected to .controlelectrode 40ithrough a bias ing resistor 59..

In; the locali oscillatorcircuit thus; described; excitation for operation during; the reception--iof frequency modulated waves is obtainedifrom the capacitancedivider comprisingthe'connectiomofi the cathode. 4,12:zto the-jcommoniterminalsyofr'cas paeitors, 52,-, 5,11. ChokeifiapEQVidfiSaa path. for: unidirectional currents between.the;catho.de and ground-forthiseonnection. Eorireceptiomofiame plitude modulated waves in a short wave band; however, when-switch. 5.8;;15 connectedgto either con act! Hm I; exci ation'zto:sustaimoscilla ns:; of ftheoscillatory-circuit .4118: providedmyi thelcone nect pnwfi he cathodetothe nt rme ia e'r i i n an-.50 0n he z riallrconncct dainductanc sa 46?. 51!.

The; OUtDUt CiICdifi-E 413 0)? the; converter? tube}: ompr s s, 611191 1? oft: seri l y onnected-iresonant:- circuits. comprising respectively; inductance 60 -:capa.cit rice. Eli and iriductancelzti and capacie tancet 3;.indu-ctances.60iand 6:2 beingthei primary. wind n f; e usnahint rmediate frequency transformers. The firstof: these circuits; iSfji nted-1 y. a; switch: 6A: which; wh n. connected to its-contact il, short theelemmtsfifl, 6i: nd-F dir t y, onnects th ement 62-.. 63: toe ground through a. by-passi capacitor $511120; at ource; f: potentials through: as: resistance 661:. When the switch: 64 vzis iconnectedzztositss contacts; I i; l J, the; l ments :60; 61b. arecconnected: inacirr it with; he;so rcerotrpot ntiatandrthe elements 62, 53 are shortecircuitedi: The elementsi cifl Bile ei u ed o t e:intermediatesfrequencyvutilized n h r ception orz-amplitude modulat d: shortw v w le heielemcnt 2. fifiziareituned oithcv nter ediate :fr quen yvutilized-iin theire eptiom of frequency mpdulatedi wavesi my receiver. circuits,-. the; various switches; are all; mechanically connectediforiunicontrolcpp i I rat o rz so hat :therr c iver; circuits: arer tunedc.

eitherior the reception of ga frequencymodulatedai wave or one 1of*twonbands;qofigiamplitudeamodu- A tedr h r i aresr he movable J-IliHET LGmQIItSt 4: ke is refierab y' el: mfiehanicallt'r her: 91 0 f qu ncy- CiIiOlJltfi antenna circuit 5 I; th iaheos a n mi t-e e u cdzsimm an *1' l11. .fr ieneies th 'zi e uenei f.t eantennarc rqu til anctiaheradiorfreeuenc t" T lw t b inei ect eat: whilerthes recamcygon the oscillatory circuit 4 is of a value to track with the antenna and radio frequency circuits to provide, in the anode circuit of'converter 3, currents of the desired intermediate frequency. When the respective circuits have their movable contacts connected to the fixed contacts 9, the receiver is adjusted for the reception of frequency modulated waves and the antenna, radio frequency and local oscillator circuits are tuned over the band of frequency modulated signals by simultaneous movement of cores l4, 3| and 41. When itis desired, however, to receive amplitude modulated signals on either of the short wave bands, the respective switches are connected to either contacts I or II depending upon the band of frequencies desired to be received. In either of these positions, the variable inductances of the antenna and radio frequency circuits are connected in series with an. inductance of a value required to resonate in the short wave bands. The values of these fixed inductances I1, 32 are such that the variable inductances I and 30 are sufficient to spread the tuning of the antenna and radio frequency circuits over the two bands of short waves.

In the local oscillator circuit 4, the value of inductance 46 required for the generation of oscillations of a frequency to track with the frequency modulated waves is such that, when the circuit is to be used to provide oscillations to track with waves in the short wave bands, the inductance 46 is connected in shunt with a portion of the inductance 5| and in series with the remainder thereof.

In Fig. 2 I have illustrated a variable inductance which is particularly adapted for tuning radio receiver circuits over the band of frequencies employed for frequency modulated short waves, as well as amplitude modulated short waves. The inductance illustrated in this figure comprises a pair of juxtaposed, peripherally incomplete loop-like metallic conductors 61, 68, each of which is provided with three complete legs and an incomplete inwardly extending leg 69. Preferably, the conductors are oriented by rotating one through an angle of- 180 with respect to the other so that the legs 69 overlap and may be joined together by means of a rivet so that the conductors are serially connected to form an inductance having a, relatively low value of self-inductance. The value of both of the self and mutual inductance of the loops 61, 68 may be varied by means of a metallic vane H formed of any suitable material, such as copper, and which is supported to be moved linearly in a plane intermediate the planes of the conductors 61, 68. Preferably, the vane H is provided with a pair of longitudinal slots 12 so shaped that a desired inductance versus displacement characteristic is obtained as the vane is moved into positions interleaving the conductors 61, 68. The loops 67, 68 are provided with a plurality of outwardly extending arms 13 which are adapted to be received in suitable recesses 14 provided in a molded insulator 15, the recesses spacing the loops laterally. Insulator 15 is provided with a longitudinal slot 16 adapted to receive the outer edge of the vane H so that the vane moves in a predetermined manner with respect to the conductors 61, 68. I have found such an inductance to be particularly adapted for use as the inductances 1, 30, 46 in receiver circuits tuned for the reception of amplitude modulated short waves and frequency modulated waves.

An important advantage of my improved tuned circuit for multi-band radio receivers is that it utilizes the same variable inductances in the reception of both amplitude modulated short waves and frequency modulated short waves where the bands of frequency and amplitude modulated waves are widely separated in the frequency spectrum. In this way, the same variable elements are used for tuning over a plurality of bands of frequencies, reducing both the cost and the complexity of the circuits required.

While I have shown one particular embodiment of my invention, it will occur to those skilled in the art that changes and modifications may be r made without departing from my invention. I

therefore contemplate by the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In a radio receiver circuit for receiving both a pair of frequency modulated waves and a pair of amplitude modulated waves of short wave length, a pair of inductances of different values, one of said inductances being variable, a plurality of trimmer capacitors, and switching means for connecting a first of said capacitors in shunt with said one inductance for tuning said receiver circuit over a first band for reception of frequency modulated waves and for connecting the other of said inductances in series circuit with said one inductance and a second of said capacitors in shunt with said series circuit to tune said receiver circuit over a second hand of frequencies for reception of amplitude modulated waves.

2. A multi-band radio receiver circuit comprising a pair of tunable circuits, each comprising a pair of inductances of different values, one of said inductances being variable, a plurality of capacitors, first switching means for one of said circuits for connecting a first of said capacitors in shunt with said one inductance for tuning said one circuit over a first band of frequencies with variation of said one inductance and for connecting the other of said inductances in series circuit with said one inductance and a second of said capacitors in shunt with said series circuit to tune said one circuit over a second band of frequencies, second switching means for the other of said circuits for connecting a first of the said capacitors thereof in shunt with the said one inductance thereof for tuning said other circuit over a band of frequencies displaced from said first band of frequencies and for connecting a portion of the other of said inductances thereof in series circuit with the said one inductance thereof and a second of the said capacitors thereof in shunt with said last series circuit to tune said other circuit over a band of frequencies displaced from said second band of frequencies.

3. In a multi-band radio receiver, a pair of tunable circuits each comprising a pair of inductances of different values, one of said inductances being variable, and a plurality of capacitors, switching means for a first of said circuits selectively connecting the other of said inductances in series circuit with said one inductance and differentof said capacitors in shunt with said one inductance to form a circuit tunable over a given band of short wave lengths or a different high frequency band widely spaced in wave length from said given band, and switching means for the other of said pair of circuits for selectively connecting a portion of the other of. the inductances: theneofi1n-= shuntvwithx the one inductance thereof and: different: of! said? capacb tor-rsainshunt with-said: one: inductance: towfbrm a: circuit: tun-able; ovenm'ngies of frequencies? displaced" by substantiallyfixed aimonntsw of ice quency respectively fromsaid gi-ven band of frequencies: and said different bands c'ffr uencies;

4; Tina multi-bandmadic'receiven circuit, a: pair ofinductances of-: different valuesi, one: ofwsaid inductancessbeing variable; apluradity ofcwpaci tors, and switching; means fonselectivelyfconnesting; wfirst of. said capacitors in' shuntl with said on'e inductance-on a seccnd of: swidmapacitdrs shunt with: said one" inductance and: said one inductance-$0 anintermedintepcinh on t'he other of said inductances to form: a' circuita tunable over aband: of short-wave: lengthsor a: bandeofihigher frequencies= displaced: from said: band of: firequencies of short wave length. 1

5r- A: tunableusysteml ion aw; multieband receiver comprising; a; pair of circuits =each--cnmprisinge tvm inductances. of different values; one of said inductances being; variable; and apainof; 0898101. tor s im'ean's in=0neoi said? circuits ion: selectively connecting oneqf said capacitors in: shuntwith said one inductance or the cthen ofsaid capaci torsin shunt with said: pairof. inductances in series; and means in the othen of said: circuits for selectively connecting oneoffl said caipacitors inv shunt the variable inductance thereof or thervariableinductance: there-0f: tc am intenmediate point -on the-f other" of the: induetances taherecf and: the: othen of the capacitors-thereof in shunt-withihe other: inductance thereoi said connecting 1 means being; arranged: for simultane ous openation and said" inductajnc'es -andh capacitors being oivalues: to fiorm circuits tunable ne spectivelwoven a -first band of short-wavelengths on a, second basnd.v 01: frequenciew displaced un war-(11y inithe fnequency spent-mm; from saidi'firat bandand rang-65 0f frequencies displacedkby sub stantially: fixediamcuntsimm said-firsjt or? second bands:

JQSEFH A2 WGRGESBE'R", Jm

CITED:

The renewing referemce's are of record" mtiie file of thiswatent'f' UNITED STATES PAFIJENTS 

